diff --git a/src/libslic3r/Format/STEP.hpp b/src/libslic3r/Format/STEP.hpp
index 397ee2c1b..71453b3fc 100644
--- a/src/libslic3r/Format/STEP.hpp
+++ b/src/libslic3r/Format/STEP.hpp
@@ -12,6 +12,7 @@ namespace fs = boost::filesystem;
 
 namespace Slic3r {
 
+class Model;
 class TriangleMesh;
 class ModelObject;